Hypertension in pregnancy is associated with increased risk of foetal growth retardation and in severe cases can lead to both maternal and foetal problems. It is the major complication of pregnancy and is one of the three leading causes of maternal death.
Hypertension in pregnant women is either a chronic condition caused by a disease unrelated to pregnancy (essential or secondary hypertension), or caused by a pregnancy induced condition known as “pre-eclampsia” (also known as “pregnancy induced hypertension”). In the former condition, elevated blood pressure is the cardinal patho-physiological feature. In pre-eclampsia, the increased blood pressure is a sign of the underlying disorder and the impact of the two conditions and their management on the mother and foetus is quite different. An attempt to differentiate these two classes of patient has led to confusion in terminology worldwide.
The circadian blood pressure (BP) variation in normal pregnancy is similar to that of non-pregnant women, with the highest value being in the morning and the lowest around midnight. A similar pattern exists in pregnancy accompanied by chronic (essential) hypertension.
In contrast, in women with pre-eclampsia, the diurnal blood pressure pattern is reversed with the maximum blood pressure occurring at night.
Pre-eclampsia is a disease of the placenta with widespread systemic effects affecting maternal renal, cerebral, hepatic and/or clotting functions. The principal clinical features include hypertension, proteinuria and oedema with any or all of these present.
While there are generally agreed risk factors for pre-eclampsia, the precise causes and mechanisms remain unproved. In addition, there are no clear indicators that are useful in predicting the occurrence or the severity of the condition. There are no known effective preventative measures and although various techniques and medications are used to limit the symptoms (in particular the hypertension), the only definitive treatment is delivery of the baby, and removal of the diseased placenta.
Pre-eclampsia usually occurs after 20 weeks gestation and most frequently near term. Pre-eclampsia (and the hypertension associated with it) is a different medical condition to essential or secondary hypertension (e.g., as illustrated by the different diurnal characteristics). The methods used to manage patients with pre-eclampsia mainly consist of closely monitoring the patient and if necessary, controlling blood pressure with medication. In severe cases, additional medications are used to prevent convulsions (eclampsia).
It has been recognised that obstructive sleep apnea (OSA) is related to elevated blood pressure. The inventor has previously demonstrated the treatment of OSA by use of Continuous Positive Airway Pressure (CPAP), and in particular nasal-Continuous Positive Airway Pressure (nCPAP). It has also been demonstrated that partial airflow limitation (upper airway resistance syndrome “UARS”) can cause elevations in blood pressure and that the blood pressure can be controlled by the use of CPAP, and in particular nCPAP. However patients with pre-eclampsia-induced hypertension may not display symptoms indicative of UARS. Accordingly, UARS symptoms in such a patient may be missed resulting in the hypertension caused by pre-eclampsia going untreated.